Impact of photocatalyst optical properties on the efficiency of solar photocatalytic reactors rationalized by the concepts of initial rate of photon absorption (IRPA) dimensionless boundary layer of photon absorption and apparent optical thickness

The concepts of “initial rate of photon absorption” (IRPA), “dimensionless boundary layer of photon absorption” and “apparent optical thickness (τapp)” are presented to evaluate the radiative transfer phenomena in solar, slurry, planar, photocatalytic reactors. The radiation field produced by suspensions of TiO2 and goethite, two photocatalysts with profoundly different optical properties used in heterogenous photocatalysis and heterogeneous photo-assisted Fenton reactions, was determined by the six-flux radiation absorption-scattering model coupled to the Henyey-Greenstein scattering phase function (SFM-HG). The concept of IRPA, defined by the differentiation at the local volumetric rate of photon absorption (LVRPA) at the reactor window boundary, is proposed as a new approach to determine the impact of catalyst loading and optical properties on the extinction of light inside a photoreactor. The IRPA showed that the extinction of light follows a second order dependency on the photocatalyst concentration while the impact of the optical properties can be expressed by a decoupled function (Ψ function). The Ψ function increased with photocatalyst concentration and approached a maximum at the same optimal photocatalyst concentration determined from the analysis of the total rate of photon absorption (TRPA) in the reactor. The analysis of TRPA and boundary layer of photon absorption redefined here in dimensionless form, as a function of τapp, determined that the most efficient rate of radiation absorption in solar powered planar reactors occurs at τapp = 4.1–4.4, with approximately 10% of the reactor width under darkness. τapp is a similarity dimensionless parameter exclusively derived from the SFM approach, which clusters the effects of photocatalyst loading, reactor dimension and photocatalyst optical properties, providing an ideal parameter for designing and scaling photocatalytic reactors operated with any kind of photocatalytic material

Coupling the Six Flux Absorption-Scattering Model to the Henyey-Greenstein scattering phase function: Evaluation and optimization of radiation absorption in solar heterogeneous photoreactors

Robust and practical models describing the radiation field in heterogeneous photocatalytic systems, used in emerging environmental, photochemical and renewable energy applications, are fundamental for the further development of these technologies. The six-flux radiation absorption-scattering model (SFM) has shown to be particularly suitable for the modeling of the radiation field in solar pilot-plant photoreactors. In this study, the SFM was coupled to the Henyey-Greenstein (HG) scattering phase function in order to assemble the model with a more accurate description of the scattering phenomenon provided by this phase function. This new version of SFM, named as SFM-HG, was developed through fitting the Local Volumetric Rate of Photon Absorption (LVRPA) determined in a flat photoreactor to the "pseudo-experimental" LVRPA calculated by a Monte Carlo (MC) approach, which included the HG expression. As a result, simple mathematical correlations describing the SFM-HG scattering probabilities as function of the HG scattering parameter were determined. The SFM-HG was validated through a comparison with the MC model predictions of the Total Rate of Photon Absorption (TRPA) in the slab photoreactor. A RMSE% of approximately 5% demonstrated satisfactory agreement between the models. The SFM-HG was further applied to evaluate the impact of selected scattering phase functions on the absorption of radiation in solar photoreactors, operated with commercial TiO2 photocatalyst. The results have established that, the apparent optical thickness, τapp (or τapp,max for tubes) a parameter derived from the SFM approach, is the most appropriate for the design and optimization of photocatalytic reactors. This parameter is insensitive to scattering albedos and phase functions. CPC, tubular and flat-plate photoreactors should be designed with τapp,max = 12, τapp,max = 7 and τapp = 4.5 respectively

Photocatalysis with Nanoparticles for Environmental Applications: Reactor Design Issues

The scale-up of photochemical or photo-catalytic processes is a hard task, requir-ing the correct definition of light distribution across the device. After a collection of examples of different photoreactor layouts adopted for water treatment, the main modelling issues are reviewed. Alternative radiation modelling approaches are compared. The reaction rate ex-pressions are presented, considering the dependence on light, catalyst and reactants distribution and including possible mass transfer limitations

Multi-Messenger observations of the γ-ray blazar 4FGL J0658.6+0636 consistent with an IceCube high-energy neutrino

The detection of cosmic neutrinos has raised many new questions in astroparticle physics, among the most compelling of which is the identification of cosmic neutrino emitters. After more than a decade of IceCube operations, the most promising neutrino astrophysical association remains the very-high-energy (VHE, > 100 GeV) blazar TXS 0506+056. Recently, on November 14, 2020 the IceCube observatory reported the detection of a well-reconstructed high-energy neutrino event, IceCube-201114A, with a high probability of being astrophysical. Within the 90% IceCube-201114A localization region only one known γ-ray (> 100 MeV) source is found. This is 4FGL J0658.6+0636, associated with the blazar NVSS J065844+063711. In these proceedings we present results from the rich multi-messenger campaign triggered by the IceCube-201114A neutrino detection, which has allowed us to collect simultaneous and quasi-simultaneous data for the γ-ray source potentially associated with the neutrino. NVSS J065844+063711 is a previously-known blazar with broadband properties resembling a high-synchrotron-peaked object, making it a promising TeV emitter. Indeed, the detection of very high-energy (VHE) photons (i.e., > 100 GeV) by the Fermi Large Area Telescope provides the first evidence of such emission from this object. It makes NVSS J065844+063711 the second VHE object found within the 90% confidence region of a well-reconstructed, high-energy IceCube event